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Blastomycosis: Differential Diagnoses & Workup
Updated: May 21, 2008
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
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Differential Diagnoses
Other Problems to Be Considered
Skin
Squamous Cell Carcinoma
Pyoderma Gangrenosum
Keratoacanthoma
Halogenoderma
Chromoblastomycosis
Tuberculosis verrucosa cutis
Lupus vulgaris
Blastomycosislike pyoderma
Bone and joints
Metastatic carcinoma
Bacterial osteomyelitis
Brain
Brain neoplasm
Workup
Laboratory Studies
- A leucocyte and differential count may show leucocytosis with a left shift, particularly in cases with a pneumonic presentation; however, the test has low sensitivity and specificity.
- Pulse oximetry is appropriate in detecting hypoxemia in cases that present as pneumonia.
- Arterial blood gases are indicated in the presence of tachypnea, pulmonary infiltrates, and hypoxemia by pulse oximetry.
- Sputum microscopy is a simple and inexpensive test that has a high diagnostic yield of more than 75% in patients with a pneumonic presentation. Place a small sample of freshly expectorated sputum on a slide and digest it with drops of potassium hydroxide. Cover it with a cover slip and examine it under a microscope. Yeasts, 8-20 micrometers in size, with single, broad-based buds, double refractile walls, and multiple nuclei are extremely characteristic of B dermatitidis. This permits the physician to begin treatment without delay.
- Microscopy of other fluids (eg, pus from skin lesions, draining fistulas, aspirate from an abscess) can be examined in a manner similar to that described for sputum to detect the fungus.
- Microscopic examination of a potassium hydroxide wet mount of pus aspirated or expressed from skin microabscesses, fistulae, or subcutaneous abscesses will reveal characteristic broad-based budding yeast. B dermatitidis also is stained by calcofluor; use of this reagent may improve the sensitivity of microscopic examination of pus.
- Sputum culture: Isolation and identification of the organism in an appropriate laboratory culture medium provides absolute confirmation of the diagnosis; however, it may be time-consuming since culture observation may occur as early as 5 days or as late as 30 days.
- Exoantigen testing and a DNA probe reduce the time for making the final identification from a culture.
Imaging Studies
- Chest radiograph
- Findings vary and lack diagnostic specificity. Alveolar infiltrates (eg, consolidation), masslike densities, and nodules are common patterns in order of frequency.
- Cavitation may be present, and there is no predilection for any lobe.
- Pleural effusion is uncommon, but pleural thickening adjacent to an infiltrate may be observed.
- Hilar or mediastinal lymph node enlargement rarely occurs.
- Chest CT scan
- This test is not needed in all cases.
- The test better defines the character and distribution of the abnormalities observed in a roentgenogram and is helpful in identifying mediastinal abnormalities and loculated pleural effusions.
- A head CT scan is useful in the detection of brain abscesses.
Other Tests
- Skin test is not reliable for diagnosis and is not commercially available.
- Serologic tests
- Complement fixation and immunodiffusion tests lack sensitivity and cannot be used to exclude the diagnosis.
- An enzyme immunoassay (EIA) for antibodies to the A antigen of B dermatitidis is a more sensitive test, and titers of greater than 1:32 strongly support the diagnosis.
- Newer tests that use more specific cell wall antigens, radioimmunoassays (RIAs), and Western blot techniques have improved sensitivity and specificity but are not yet available for widespread clinical use.
Procedures
- Bronchoscopy (with washings, brushings, and a biopsy) is indicated in the following situations:
- Absence of sputum
- Nondiagnostic sputum microscopic examination
- Undiagnosed pulmonary mass density, atelectasis, or consolidation
- Hemoptysis
- Percutaneous needle or surgical biopsy of affected organ, such as skin lesions, subcutaneous nodule, bone, or laryngeal lesion
- Prostatic massage: In cases of blastomycosis of the genitourinary tract, the urine collected after a massage is likely to have a higher diagnostic yield.
- Lumbar puncture: Diagnostic yield of examination of cerebrospinal fluid is low in CNS blastomycosis; however, ventricular fluid specimens have a higher yield.
Histologic Findings
The yeast forms are best visualized with a periodic acid-Schiff (PAS) stain, and they are not easily observed with a hematoxylin and eosin (H&E) stain. The methenamine silver and Papanicolaou are other reliable stains. Demonstration of the yeasts is particularly important in blastomycosis that involves sites with squamous epithelium (eg, skin, larynx, trachea) since the hyperplastic response observed in the tissue may simulate squamous cell carcinoma.
Skin lesions of disseminated blastomycosis are characterized by pseudoepitheliomatous hyperplasia of the epidermis, intraepidermal microabscesses, and a suppurating granulomatous reaction in the dermis.
The hyperplastic epidermis lacks the cytological atypia of squamous cell carcinoma. Intraepidermal abscesses contain abundant neutrophils and organisms; organisms are best visualized with the diastase-digested periodic acid-Schiff staining procedure or with the methenamine silver stain. Yeasts are present extracellularly in the dermis or intracellularly in multinucleated giant cells. Intracellular yeasts are easily identified on routine hematoxylin and eosin-stained sections of skin as punched-out "holes" in cytoplasm of the giant cells. The inflammatory infiltrate is polymorphous, containing lymphocytes, histiocytes, and neutrophils. Tuberculoid granuloma formation is unusual, but if it occurs, it is not accompanied by caseation.
More on Blastomycosis |
| Overview: Blastomycosis |
 Differential Diagnoses & Workup: Blastomycosis |
| Treatment & Medication: Blastomycosis |
| Follow-up: Blastomycosis |
| Multimedia: Blastomycosis |
| References |
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References
Rooney PJ, Sullivan TD, Klein BS. Selective expression of the virulence factor BAD1 upon morphogenesis to the pathogenic yeast form of Blastomyces dermatitidis: evidence for transcriptional regulation by a conserved mechanism. Mol Microbiol. Feb 2001;39(4):875-89. [Medline].
Klein BS, Vergeront JM, Weeks RJ, Kumar UN, Mathai G, Varkey B, et al. Isolation of Blastomyces dermatitidis in soil associated with a large outbreak of blastomycosis in Wisconsin. N Engl J Med. Feb 27 1986;314(9):529-34. [Medline].
Pappas PG, Threlkeld MG, Bedsole GD, Cleveland KO, Gelfand MS, Dismukes WE. Blastomycosis in immunocompromised patients. Medicine (Baltimore). Sep 1993;72(5):311-25. [Medline].
Pappas PG, Pottage JC, Powderly WG, Fraser VJ, Stratton CW, McKenzie S, et al. Blastomycosis in patients with the acquired immunodeficiency syndrome. Ann Intern Med. May 15 1992;116(10):847-53. [Medline].
Meyer KC, McManus EJ, Maki DG. Overwhelming pulmonary blastomycosis associated with the adult respiratory distress syndrome. N Engl J Med. Oct 21 1993;329(17):1231-6. [Medline].
Sugar AM, Liu XP. Efficacy of voriconazole in treatment of murine pulmonary blastomycosis. Antimicrob Agents Chemother. Feb 2001;45(2):601-4. [Medline].
Abuodeh RO, Chester EM, Scalarone GM. Comparative serological evaluation of 10 Blastomyces dermatitidis yeast phase lysate antigens from different sources. Mycoses. Apr 2004;47(3-4):143-9. [Medline].
Chapman SW, Bradsher RW Jr, Campbell GD Jr, Pappas PG, Kauffman CA. Practice guidelines for the management of patients with blastomycosis. Infectious Diseases Society of America. Clin Infect Dis. Apr 2000;30(4):679-83. [Medline].
Davies SF, Sarosi GA. Epidemiological and clinical features of pulmonary blastomycosis. Semin Respir Infect. Sep 1997;12(3):206-18. [Medline].
Varkey B. Blastomycosis in children. Semin Respir Infect. Sep 1997;12(3):235-42. [Medline].
Further Reading
Keywords
blastomycosis, Gilchrist disease, Gilchrist's disease, fungal infection, fungus infection, Blastomyces dermatitidis, B dermatitidis, pulmonary infection, adult respiratory syndrome, ARDS, antifungal treatment
